The present invention relates to methods and mechanisms for continuous control and trim of the floating position of a fast moving, planing or semi-planing ship hull during acceleration and propulsion at cruising speed.
The need for higher speeds during sea transportation has lately produced a plurality of technical improvements. The primary goal of these improvements has been to reduce the drag during the forward propulsion of the ship, and thus the need for power at higher speeds. Some of these improvements have in common that the wet surface is reduced, and therefore the frictional drag is reduced. "Wet surface" as referred to herein should be understood as the part of the ship hull that is in contact with the water surface or the part that is submerged below the water surface.
Beside the need for higher speeds, there is also a growing need for improved comfort of passengers.
Conventional fast moving and planing typically have the center of gravity positioned aft of the mid section of the ship. This type of hull makes the ship sensitive to pitching, i.e. vertical oscillating movements in the longitudinal extension of the ship hull. These movements may cause the stem to oscillate vertically in an accelerated manner, while the stern remains relatively stationary.
Another problem, that is related to fast moving and planing ships, is the difficulty of achieving an optimal operational angle between the keel or the bottom of the ship hull and the surface of the water. An optimal operational angle or attitude is generally about 5.degree.. Ship hulls that operate with such an operational angle have the center of gravity far behind the mid section of the ship hull and have, therefore, little or non-existent longitudinal stability. In practice, these types of ship hulls are only suitable for racing. Even if a dynamic trim angle of about 5.degree. is attainable in certain designs, it is often impractical due to problems related to navigation, handling of goods and the comfort of passengers.
A technology that, in many aspects, satisfies the requirements of reduced drag and wet surface in this type of ship hulls is the use of support planes or hydro foils which may be submerged or sliding on the water.
The existing systems of submerged support planes are all directed to having a support plane only at the stem of the ship hull and, in the alternative, to having support planes both at the stem and at the stern of the ship hull, The former is only moderately efficient and the latter requires expensive and complex systems, One problem with designing a system having support planes both at the stem and the stern is the trough or the wake between two waves that is generated by the front support plane. This interferes with the function and efficiency of the rear support plane, resulting in increased drag.